1. Technical Field of the Disclosure
The present embodiment is related in general to electromagnetic waveguide interconnection systems, and in particular to a self-keying and orientation system to establish a repeatable waveguide calibration and connection for millimeter wave and sub-millimeter wave applications.
2. Description of the Related Art
Waveguides are used to transmit electromagnetic wave energy such as X-Rays, visible light, or sound waves from one point to another. The waveguide type is selected depending on the frequency of the wave to be propagated. The most common waveguide design is a simple hollow metal conductor tube inside which the wave travels, eventually exiting and propagating outward and away from the exit point of the tube. For transmitting waves through different mediums, a special type of waveguide is employed. This type of waveguide wherein the wave is kept in a confined medium includes, for example, air-filled waveguides, dielectric filled waveguides, slot-line waveguides, slot-based waveguides, and others. In these systems, the waveguide interface is the only physical means to connect different waveguide components together to allow the waves to propagate therethrough.
In waveguide applications, accurate and repeatable measurements depend on the quality of interface used. The use of calibration kits is necessary for removing systematic errors and thereby increasing the accuracy of measurements. The components of the calibration kit interface are a crucial factor in the calibration success. Conventional waveguide systems employ mechanical clamps with waveguide interfaces to efficiently transmit electromagnetic waves through the waveguide. Typical waveguides are made from materials such as brass, copper, silver, aluminum, or any other metal exhibiting low bulk resistivity. Waveguide structures have conventionally been assembled in several ways. Dip-brazing is a process for joining aluminum waveguides. A thin doping layer is applied at the point of connection, thereby lowering the melting point at that one contact point so the waveguides may be joined. Electroforming allows the entire waveguide structure to be built up layer by layer through electroplating. Other methods include electronic discharge machining and computerized numerically controlled machining.
Waveguides are becoming more commonly used in the millimeter wave and sub-millimeter wave industry, which includes frequencies above 30 GHz. This high band of electromagnetic waves is beginning to be used on many new devices and services, such as high-resolution radar systems, point-to-point communications, and point-to-multipoint communications. Higher frequency waves require a smaller waveguide, meaning that for millimeter wave and sub-millimeter wave ranges, the waveguides must be machined very precisely. At the smallest sizes even the highest machining tolerances conventionally available begin to present problems. The effect of waveguide misalignment is degraded electrical performance of the waveguide, such as increased voltage standing wave ratio (VSWR). The more accurately the waveguide interfaces are aligned, the better behaved and more predictable is the waveguide system performance.
The most common and accurate 2-port waveguide calibration system uses the Thru-Reflect-Line (TRL) calibration connection. The thru portion of the system simply connects the two independent waveguide reference planes together. The reflective portion of the system which includes a mirror finish metal, connects a waveguide short to each of the reference planes, while the line portion of the system connects a shim of predetermined length between the two independent reference planes. In the thru condition, each of the reference planes' waveguide apertures needs to be matched perfectly to each other. For the reflective condition, the only requirement is to have a material with mirror-like finish at the interface to reflect all incident electromagnetic waves. In the line condition, the shim's waveguide aperture must match both waveguide reference planes' apertures simultaneously.
Another conventional means for interfacing waveguide apertures between different waveguide sections uses two fixed outer alignment pins disposed opposite one another on a circular waveguide interface. The tolerances of this alignment method are too loose for many applications and result in unacceptable levels of mismatches in some millimeter wave applications. To correct for this, a more advanced system uses removable alignment pins having much tighter tolerances. The removable alignment pins are generally located just above and below the waveguide aperture. In applications that approach sub-millimeter wave frequencies, even the removable center alignment pins of a relatively tighter tolerance have proven to be insufficient to maintain an adequately aligned aperture interface. The Lau-Denning interface disclosed in U.S. Pat. No. 7,791,438 issued to Lau on Sep. 7, 2010, hereinafter referenced below as “The Lau-Denning interface”, addresses the critical single interface connection mismatch issue but lacks a clear definition of addressing the multiple interface single connection such as the shim in the TRL calibration.
Based on the foregoing there is a need for an improved waveguide interface that offers a solution to the multiple interface single connection issue unresolved by the Lau-Denning interface. The needed waveguide interface would provide a reliable self-keying and orientation system for establishing a repeatable waveguide calibration and connection. In addition, the needed system would provide a visual aid to a user to ensure that a flange interface polarity is maintained and that angular rotation is aligned to within less than 1°. Finally, the needed system would be able to provide a solution for accurate waveguide interface without the use of alignment pins or any other types of alignment mechanism.